Welcome to SR
I am sorry for the pain that your mothers choices are causing you. I would suggest you also post in our friends and families of substance abusers forum. There are people there who would be experienced in these types of matters.
I wish I was able to give you some answers. The only thing that I know is that taking medications that are not prescribed or taking medications not as prescribed is an indicator of abuse of that medication. Does that mean she is addicted? That is a question only she can answer.
You also might consider going to ALATEEN. It is a group to help teenagers deal with a drunk or addicted parent. If you are not a teenager then I would suggest ALANON. It is a group for adults with alcoholics/addicts in their lives.